1. Field of the Invention
The present invention generally relates to an apparatus for protecting an automobile or motor vehicle against unauthorized operation thereof and particularly to an antitheft apparatus which allows operation of an internal combustion engine of a motor vehicle to be started while confirming the authenticity of an identification code inputted from an engine key upon starting of the engine. More particularly, the present invention is concerned with a motor-vehicle antitheft apparatus which can ensure higher security for the protection of a motor vehicle against unauthorized operation by complicating the identification code (hereinafter referred to as the ID code for short).
2. Description of Related Art
Heretofore, when a motor vehicle or automobile is started, an engine operation starting switch is turned on by using a mechanical cylinder key (hereinafter also referred simply to as the key) delivered by the dealer to the user who is authorized to drive the motor vehicle, for the purpose of protecting the automobile against unauthorized operation for a wrong purpose such as theft. However, because such key can effectively be copied or forged relatively easily, the antitheft function as desired can not be achieved.
As an approach for reinforcing or enhancing the antitheft function, there has already been proposed such an arrangement that an ID code identifying a key specific to a motor vehicle of concern is transmitted to a key cylinder assembly installed in the motor vehicle upon insertion of the key, whereupon the ID code as inputted is discriminatively identified to be subsequently sent to a code collating means. When the ID code is decided to be an authentic ID code, the code collating means then sends an engine start enabling signal to an engine starting means. Such system is disclosed, for example, in Japanese Unexamined Patent Application Publication No. 15141/1992 (JP-A-4-15141).
More specifically, in the antitheft apparatus for a motor vehicle disclosed in the publication mentioned above, the engine start enable signal transmitting circuit is implemented in such an arrangement that the key cylinder installed in the motor vehicle is provided with a rotor coil wound on an annular core which is disposed around a key insertion slot or key hole formed in the key cylinder, while a key coil is wound on an axial core interiorly of the key. Thus, by inserting the key into the key cylinder, an electromagnetic induction circuit is formed by the key coil and the rotor coil positioned close to each other. Thus, under the action of the electromagnetic induction between the both coils, the ID code can be transmitted to the key cylinder. In response, the key cylinder sends the ID code as received to the code collating means.
When the ID code as received is decided to be justifiable or authentic by the code collating means, an engine start signal is generated to be sent to an engine operation start decision means. As such motor-vehicle antitheft apparatus that is arranged for making decision as to whether the engine start operation is to be inhibited (disabled) or allowed (enabled) on the basis of the ID code stored in the key, there is known a motor-vehicle antitheft apparatus of such a structure as shown in FIG. 9. For having a better understanding of the background technology of the invention, this known motor-vehicle antitheft apparatus will be described in some detail.
Referring to FIG. 9, a cylinder key 1 used for starting an internal combustion engine (hereinafter also referred to simply as the engine) of a motor vehicle has a manipulating head 1a which incorporates as embedded therein a key coil antenna 1a.sub.1 serving for both functions of an induction coil in which a voltage is induced under the electromagnetic induction, an antenna for effectuating radio communication and an integrated circuit (also referred to as IC in abbreviation) 1a.sub.2 which includes a nonvolatile memory (e.g. electrically erasable programmable read-only memory or EEPROM in abbreviation, not shown) for storing an ID code which is inherently allocated to the key 1, and a control circuit for signal transmission and reception.
On the other hand, a key cylinder 2 mounted on the motor vehicle in a cab thereof is provided with a keyhole 2a.sub.1 into which a key blade 1b (i.e., a main body of the cylinder key 1) is to be inserted, wherein there is provided around the keyhole 2a.sub.1 a key cylinder coil antenna 2a.sub.2 which serves not only as an induction coil for inducing a voltage in the key coil antenna 1a.sub.1 incorporated in the key head portion 1a in the inserted state thereof but also as an antenna for performing a signal communication with the key coil antenna 1a.sub.1 by making use of the electromagnetic induction taking place between the coils 1a.sub.1 and 2a.sub.2. By inserting the key blade 1b into the key cylinder 2 and rotating it, an ignition key switch 2b is closed to thereby transmit a power-on signal SG and other demanded signals such as command signals to an engine control unit or ECU incorporating a code collating means 3, an engine start decision means 5 and others.
The code collating means 3 is put into operation in response to the power-on signal SG generated by the ignition key switch 2b. As can be seen in FIG. 9, the code collating means 3 is comprised of a power source 3a for supplying a voltage to various constituent parts of the code collating means 3 in response to the power-on signal SG inputted from the ignition key switch 2b, a radio frequency circuit (hereinafter also referred to as the RF circuit) 3c for sending a high frequency signal destined for the electromagnetic induction to the key cylinder coil antenna 2a.sub.2 while receiving the ID code signal sent out from the key 1 through the key cylinder coil antenna 2a.sub.2 under the action of the electromagnetic induction, a control unit 3b for comparing the ID code as inputted with an ID code stored in an electrically erasable programmable read-only memory (hereinafter referred to as the EEPROM in abbreviation) 3e for generating and outputting an engine operation starting signal when coincidence is determined between the input ID code and the stored ID code, and a communication interface 3f for allowing a signal (engine start enabling signal or engine start disabling or inhibiting signal) SE to be transferred between the code collating means 3 and the engine operation start decision means 5.
On the other hand, the engine start decision means 5 includes a communication interface 5.sub.1 for realizing the signal transfer (i.e., signal input/output) with the code collating means 3 and a control unit 5.sub.2 incorporated in the engine starting means 5 for making decision as to coincidence between the engine start enabling signal SE as received and a corresponding signal stored previously in an EEPROM 5.sub.4, to thereby output the engine start enabling or disabling signal to an engine operation starting means 7 in dependence on the result of the coincidence decision mentioned above.
Next, description will turn to operation of the motor-vehicle antitheft apparatus of the structure described above. For starting operation of the engine of the motor vehicle, the operator or driver inserts the cylinder key 1 into the key cylinder 2 and rotates the key 1 in an attempt to start the engine. As a result of this, the contact of the ignition key switch 2b is chaned over to a position at which the power-on signal SG is supplied to the code collating means 3 and the engine start decision means 5. In response to the input of the power-on signal SG, the power source 3a operates to supply to the control unit 3b electric power from an onboard battery (not shown).
When the control unit 3b is put into operation in response to the supply of the electric power, the RF circuit 3c sends a high frequency signal to the key cylinder coil antenna 2a.sub.2 for excitation thereof, as result of which an electric current or voltage is induced in the key coil antenna 1a.sub.1 incorporated in the cylinder key 1 under the effect of electromagnetic induction excited by the key cylinder coil antenna 2a.sub.2.
Upon application of the induced voltage to the IC (integrated circuit) 1a.sub.2, a capacitor incorporated in the IC 1a.sub.2 is electrically charged to serve as a power source for the IC 1a.sub.2. During a period in which the capacitor is being charged, the coil antennas 1a.sub.1 and 2a.sub.2 are used as the antennas for signal transmission/reception. To this end, sending of the high frequency signal from the RF circuit 3c to the key cylinder coil antenna 2a.sub.2 is stopped under the control of the control unit 3b. The time point at the sending of the high frequency signal is stopped is detected by the control unit 3b. During the period in which the sending of the high frequency signal is stopped, the IC 1a.sub.2 reads out the ID code inherently allocated to the key 1 from the non-volatile memory (e.g. EEPROM, not shown) and converts it into a signal suited for transmission, which signal is then transmitted to the key cylinder coil antenna 2a.sub.2 via the key coil antenna 1a.sub.1 under the electromagnetic induction.
The signal mentioned just above is then received by the RF circuit 3c and digitized by the control unit 3b to be converted to a digitized ID code, which is then collated or matched by the control unit 3b with a verification code stored previously in the EEPROM 3e. When the collation shows a discrepancy between both the codes mentioned above, the engine start disable or inhibit signal SE is transmitted to the engine starting system 5 via the communication interface 3f, whereby the engine of the motor vehicle is inhibited from starting.
On the other hand, when coincidence is detected between both the codes mentioned above, the control unit 3b generates an engine start signal SE by adding the ID code with a rolling code which is updated newly in response to a corresponding signal supplied from the engine start decision means 5, every time the ignition key switch 2b is turned off, wherein the engine start signal SE as generated is sent to the control unit 5.sub.2 of the engine start decision means 5 through the communication between the interface units 3f and 5.sub.1.
In response to the engine start signal SE as received, the control unit 5.sub.2 compares the ID code and the rolling code contained in the engine start signal SE with those stored in the EEPROM 5.sub.4 to thereby decide coincidence or discrepancy between them. When discrepancy is detected, the control unit 5.sub.2 sends the engine start inhibit or disable signal to the engine operation starting means 7. On the contrary, upon decision of coincidence, the control unit 5.sub.2 sends to the engine start enable signal to the engine operation starting means 7, whereupon operation of the internal combustion engine of the motor vehicle is started.
The structure of the hitherto known motor-vehicle antitheft apparatus described above is certainly effective for preventing unauthorized attempt for operating the motor vehicle such as stealing by monitoring and deciphering the communication signal(s) transferred between the code collating means and the engine start decision means to thereby illegally start the engine with the engine start signal. However, the engine start decision means 5 requires to this end an EEPROM which is an external memory for storing the rolling code received in a preceding cycle in order to execute the coincidence decision processing for detecting coincidence between the rolling code contained in the engine start enable signal currently sent from the code collating means 3 and the rolling code sent in the preceding cycle.
Such being circumstances, two EEPROMs, i.e., one incorporated in the engine starting means and the other incorporated in the code collating means are indispensably required, which of course increases the cost of the system as a whole, giving rise to a problem. Besides, there may arise another undesirable situation that upon occurrence of erroneous decision of the rolling code due to temporary or transient communication error between the code collating means 3 and the engine start decision means 5, operation of the internal combustion engine of the motor vehicle can not be started even when an authentic key is used, thus involving eventually degradation in the system reliability.